Since nobody else is going to restart our hw_queue for us, theblk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficientnecessarily sufficient to ensure that the queue will get started again.In case of global resource outage (-ENOMEM because mapping failure,because of swiotlb full) our virtqueue may be empty and we can getstuck with a stopped hw_queue.

Let us not stop the queue on arbitrary errors, but only on -EONSPC whichindicates a full virtqueue, where the hw_queue is guaranteed to getstarted by virtblk_done() before when it makes sense to carry onsubmitting requests. Let us also remove a stale comment.